Buying advice on an IP camera system

Looking for some market intel on making a small investment (<500eur) for an IP camera installation in a domestic environment. Only contact me if you know the market and if you want to help me find the best solution for my needs. Not interested to buy new items, will be looking for local second hand options. Current systems i have in my house are synology ds215+, knx system, homey pro, google nest hub, unifi mesh internet.